mem: Add CleanEvict and Writeback support to snoop filters

This patch adds the functionality to properly track CleanEvicts and
Writebacks in the snoop filter. Previously there were no CleanEvicts, and
Writebacks did not send up snoops to ensure there were no copies in
caches above. Hence a writeback could never erase an entry from the
snoop filter.

When a CleanEvict message reaches a snoop filter, it confirms that the
BLOCK_CACHED flag is not set and resets the bits corresponding to the
CleanEvict address and port it arrived on. If none of the other peer
caches have (or have requested) the block, the snoop filter forwards
the CleanEvict to lower levels of memory. In case of a Writeback
message, the snoop filter checks if the BLOCK_CACHED flag is not set
and only then resets the bits corresponding to the Writeback
address. If any of the other peer caches have (or has requested) the
same block, the snoop filter sets the BLOCK_CACHED flag in the
Writeback before forwarding it to lower levels of memory heirarachy.

1 files changed, 18 insertions, 2 deletions

diff --git a/src/mem/snoop_filter.hh b/src/mem/snoop_filter.hh
index 1e7add660..ee2c82b6e 100755
--- a/src/mem/snoop_filter.hh
+++ b/src/mem/snoop_filter.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 ARM Limited
+ * Copyright (c) 2013-2015 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -203,6 +203,11 @@ class SnoopFilter : public SimObject {
         SnoopMask holder;
     };
     /**
+     * HashMap of SnoopItems indexed by line address
+     */
+    typedef m5::hash_map<Addr, SnoopItem> SnoopFilterCache;
+
+    /**
      * Convert a single port to a corresponding, one-hot bitmask
      * @param port SlavePort that should be converted.
      * @return One-hot bitmask corresponding to the port.
@@ -222,8 +227,19 @@ class SnoopFilter : public SimObject {
     SnoopList maskToPortList(SnoopMask ports) const;
 
   private:
+
+    /**
+     * Removes snoop filter items which have no requesters and no holders.
+     */
+    void eraseIfNullEntry(SnoopFilterCache::iterator& sf_it);
     /** Simple hash set of cached addresses. */
-    m5::hash_map<Addr, SnoopItem> cachedLocations;
+    SnoopFilterCache cachedLocations;
+    /**
+     * Variable to temporarily store value of snoopfilter entry
+     * incase updateRequest needs to undo changes made in lookupRequest
+     * (because of crossbar retry)
+     */
+    SnoopItem retryItem;
     /** List of all attached slave ports. */
     SnoopList slavePorts;
     /** Cache line size. */